In the related art, as a type of an electric rotation device, there has been proposed a device including a motor and a reduction gear mechanism that reduces a rotation of the motor and transmits the rotation to a rotation shaft of a toilet seat (toilet lid) (for example, refer to JP 2010-246880A (Reference 1)).
In such an electric rotation device, in order to detect the opening and closing position of a toilet seat (toilet lid), there is a case where a rotational position sensor (for example, rotary potentiometer, rotary encoder, and the like) that meshes a rotational position detection gear with a transmission gear of a reduction gear mechanism and outputs a signal corresponding to a rotational position of a rotational position detection gear is provided. In this case, since the tooth serving as a reference of a meshing position with respect to the transmission gear is determined for the rotational position detection gear, it is required to prevent erroneous assembly from occurring when an operator assembles the rotational position detection gear in an assembling step.
Thus, a need exists for an electric rotation device which is not susceptible to the drawback mentioned above.